In recent years, a variety of traffic accidents are increasing with the increase in the number of road transport vehicles, and it is necessary to protect vehicle drivers and fellow passengers from these accidents. Therefore, at present, in many countries, vehicle's seat occupants are obligated to wear seat belts in order to prevent them from getting hurt or being physiologically injured. In general, a seat belt comprises a webbing for restraining a seat occupant, a buckle for wearing this webbing, and a retractor for controlling the unwinding and winding of the webbing. A variety of contrivances are exercised on the retractors for controlling the unwinding and winding of the webbing. As for such retractors for seat belts, there are Automatic Locking Retractors (ALR) wherein when the unwound webbing is once rewound operationally it cannot be pulled out any longer, and Emergency Locking Retractors (ELR) wherein arrangement is made such that when the acceleration exerted on the vehicle body is detected and it has increased to a predetermined value, the webbing cannot be pulled out any longer. A good many kinds of such retractors are already put on the market. Further, child restraining devices for child passengers have already been marketed. These child restraining devices are used by securing each of them onto a common seat by means of a seat belt. In this case, it is necessary from the viewpoint of safety to fixedly secure the child restraining device to a common seat prior to putting it to use. In such a case, the purpose of fixing the child restraining device securely onto the seat can readily be achieved by using a seat belt having an ALR function wherein when the webbing is once rewound it cannot be pulled out any longer. In contrast thereto, in case the child restraining device is fixedly secured onto a seat in the vehicle by means of a seat belt having ELR function, the vibration of the vehicle when it is running causes a relative motion between the child restraining device and the seat to which it is attached, and as a result, the seat belt tends to be unwound gradually from the retractor and get loose thus causing a condition in which the child restraining device is not fixedly secured by the seat belt. Therefore, to avoid such a risk, in case of fixedly securing the child restraining device to a seat by a seat belt having ELR function, it becomes necessary to carry out operations such as fixing the child restraining device to the seat securely in the condition the whole webbing is pulled out from the retractor and winding the remaining part of the webbing round a locking clip, thus requiring a very troublesome operation to attach the child restraining device to a common seat. For such reasons, in case of fixedly securing the child restraining device to a seat in the vehicle, it is convenient and recommendable from the viewpoint of safety to use a seat belt of ALR type.
However, the seat belts of ALR type are arranged when the webbing is once rewound, it cannot be pulled out any longer, and so in case there is no need of securing the child restraining device in the vehicle; that is to say, in case adult passengers occupy the seats in the vehicle, the use of seat belt of this type restrains the seat occupant always to his seat so as not to allow him to move his body freely thus letting him to feel uncomfortable when he is wearing the seat belt during the running of the vehicle.
In view of such situations, there has been developed in recent years a retractor for seat belts which can fulfill both ALR and ELR functions and which can be used selectively to fulfill either ALR or ELR function in such a manner that when the whole webbing is pulled out from the retractor it may function as ALR type seat belt, whilst in other conditions it may function as ELR type seat belt. For example, reference is to be made to U.S. Pat. Nos. 4,436,255, 4,583,701 and 4,597,546. 4,436,255 discloses a retractor for seat belts which comprises, in combination, a retractor comprised fundamentally of a ratchet wheel fixed on a webbing take-up shaft and a pawl engageable with the ratchet wheel so as to stop the unwinding rotation of the webbing from the take-up shaft; an inertia lock mechanism; and cam means which is comprised of a cam member and a follower member, the arrangement being made such that when the whole webbing is pulled out to restrain the occupant the pawl is engageable with the ratchet wheel, and when the webbing is unwound by a predetermined amount from the take-up shaft, the take-up shaft is rotatable freely in either direction, but when the inertia lock mechanism is actuated in a vehicular emergency situation the rotation of the take-up shaft is stopped. U.S. Pat. No. 4,583,701 discloses a retractor for seat belts which comprises an emergency locking retractor for a seat belt provided with an acceleration sensor; and a special cam ring, the arrangement being made such that when the whole webbing is unwound from the take-up shaft an automatic locking means is actuated. Further, U.S. Pat. No. 4,597,546 discloses a retractor for seat belts which comprises an emergency locking retractor for a seat belt provided with an acceleration sensor; a take-up shaft for winding a webbing thereon; a locking wheel connected with the take-up shaft so as to be rotated at a reduced speed relative thereto; and a special control means, and which is arranged such that when the whole webbing is unwound it may also function as an automatic locking retractor.
These automatic-emergency locking retractors comprise, in combination, a retractor which is operable fundamentally as an emergency locking retractor, and a special mechanism and which is arranged such that it may also function as an automatic locking retractor under a certain condition. However, the retractors having both ELR and ALR functions cannot operate as ALR unless the whole webbing is unwound, and in case the seat occupant does not know that the conversion of function from ELR to ALR takes place only when the whole webbing is unwound, he wears the seat belt by pulling out the webbing by a proper amount, and as a result, the retractor can be used only as ELR. In particular, in case the retractor of this type is used to fix a child restraining device onto a common seat by such a method, it can be used only as an emergency locking retractor, and therefore, there has been a problem of safety in that the webbing tends to get loose when the vehicle is running.
Thus, the prior art automatic-emergency locking retractors for seat belts can function only as ELR depending on the method of use. Therefore, it has been demanded to develop a new automatic-emergency locking retractor which can overcome such disadvantages and can always fulfill both the ELR and ALR functions.